Photographic copying process



United States Patent PHOTOGRAPHIC COPYING PROCESS Anthony ErnestJackson, London, England, assignor, by mesne assignments, to EastmanKodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing.Application September 18, 1952, Serial No. 310,357

3 Claims. (Cl. 955.6)

This invention consists in a photographic copying process, in which aline or half-tone image comprising unhardened gelatine forming part of asilver halide-type photographic emulsion coated on a first support istransferred by contact to a second support after the gelatine comprisedby the complementary image has been rendered relatively non-transferringby hardening, after or during gaslight or bromide paper may be used inthe process.

A variety of surfaces may be used as the second support, including thoseof paper, cellulose acetate, cellulose nitrate, glass, wood, syntheticresin and metal; woven fabric such as cotton or linen cloth may also beused where high resolution is not important.

For transferring the non-hardened image from the first to the secondsupport the normal methods of transferring gelatine images may beemployed, with the exception that an elevated temperature, preferably of751l0 F., should be maintained to soften the unhardened gelatine. Wherethe first support is paper, this may be squeegeed onto the secondsupport, preferably after wiping or blotting otf surplus Water, heatedand then peeled off.

In the application of this invention to the speedy reproduction ofdocuments, tracings and the like, an unhardened silver halide emulsionon a flexible first support such as paper is exposed to the originalsubject matter to be copied by contact, refiectographic, projection orcamera exposure, as appropriate, and the exposed emulsion is developedin a tanning developer, followed by development, if necessary underconditions of bright illumination, or after such illumination, in anon-tanning developer. This results in the formation of complementaryblack images, one of hardened and the other of unhardened pigmentedgelatine and, by pressing the image layer into intimate contact with asecond support such as paper and with the application of heatsufi'icient to soften the unhardened emulsion, the latter can betransferred to the second support. The two supports can then be pulledapart to leave, on the one hand, a negative of the original subjectmatter on the first support and, on the other hand, a correspondingpositive on the second support, neither of which requires fixing bysodium thiosulphate.

The process described in the preceding paragraph can be modified byomitting the treatment of the image layer on the first support with anon-tanning developer. The image transferred to the second support willthen comprise silver halide Which can be developed in situ, after orduring exposure to light, by a developer, which need not be of theselective reducing agent type. Use of a tanning developer would give ahardened image on the second support.

Where the original subject matter copied as described in either of thetwo preceding paragraphs is a negative, the image transferred to thesecond support will also be a negative. Sometimes, however, it isdesired to provide, on a given support, a positive copy of a negativesub- 2,704,712 Patented Mar. 22, 1955 ject matter or vice versa, andthis can easily be effected by reversing the order of treatment with thetanning and non-tanning developers. Thus, the image formed by exposureof the emulsion to the original subject matter is developed in theordinary way with a non-tanning dcveloper, and then the complementaryimage is developed in a tanning developer, during or after exposure tolight. The transferable image will then be a negative relative to theoriginal subject matter.

In the application of this invention to the production of printingplates including rollers, particularly planographic plates for offsetprinting, the second support is constituted by a printing plate and thetransferred image is hardened. As already mentioned, this hardening canconveniently be effected by transferring the unhardened image in anundeveloped state, and subsequently treating it, after or duringexposure to light, with a tanning developer. Alternatively, whether ornot the image has been developed before transfer, it may be treated onthe second support with a conventional hardening agent such as potashalum, chrome alum orformaldehyde. In either case, the image may beemployed as a lithographic ink acceptor or as a resist for etchingpurposes.

Where the image transferred to the second support is in the form of anundeveloped silver halide emulsion this may, if desired, be freed fromsilver by hardening and then treating with a silver halide solvent suchas an alkali cyanide or thiosulphate. Alternatively, use may be made oftoning, colour development, bleaching and a variety of other knowntreatments to obtain special effects.

In carrying out the process of this invention, the developer used first,whether of the tanning or non-tanning type, will necessarily be of theselective reducing agent type, so that the exposed areas are deplenishedin silver halide whilst the complementary areas remain unaffected. Anysubsequent development effected with a non-tanning developer, and anyeffected on the emulsion after transfer may, however, be carried outwith a non-selective agent not requiring a second exposure, andreferences herein to developers should be construed accordingly.Wherefon the other hand, the first development does not effecthardening, any subsequent development before transfer is preferablyeffected with a tanning developer of the selective reducing agent typeto avoid the possibility of reaction with undeveloped silver halidewhich might be left in the previously developed image areas withconcomitant hardening of the gelatine it is required to transfer. Thus,in copying a tracing, a contact print on gaslight paper may be treatedfirst with a tanning developer and then with aqueous sodium sulphide,followed by transference, a second exposureibeing unnecessary.

The following example illustrates one manner of carrying this inventioninto effect.

A document paper coated with an unhardened silver halide emulsionpossessing characteristics suitable for re fiectographic printing washeld face down in contact with an original document and illuminated fromthe back of the paper through a yellow filter for approximately 20seconds using a watt lamp at a distance of 30 inches from the paper. Theresulting exposed negative was then developed for l /2-2 minutes in atanning developer made up from 10 ccs. each of solutions A and B and 230ccs. of water, the solutions having the following composition:

Grams A. Pyrocatechin 50 Potassium bromide 5 Potassium metabisulphite 5Water to make 500 ccs.

B. Potassium carbonate 200 Water up to 500 ccs.

gelatino silver halide emulsion on a flexible support, to form a latent"image of said subject mattertherein, developing the said latent image ina non-tanning developer to yield an unhardened negative image, exposingthe emulsion to light and developing a complementary latent image on thesame support in a tanning developer, transferring the said negativeimage to a second flexible support by pressing the said image intointimate contact therewith at a temperature at which the unhardenedemulsion softens and separating the two supports.

2. A photographic copying process which comprises exposing to subjectmatter to be copied an unhardened gelatino silver halide emulsion on aflexible support, to form a latent image of said subject matter therein,developing the said latent image in a non-tanning developer to yield anunhardened negative image, exposing the emulsion to light and developinga complementary latent image on the same support in a tanning developer,transferring the said negative image to a second flexible support bypressing the said image into intimate contact 20 therewith at atemperature at which the unhardened emulsion softens and separating thetwo supports and thereafter hardening the gelatme of the image sotranserre 3. A photographic copying process which comprises exposing tosubject matter to be copied an unhardened 'gelatino silver halideemulsion on a flexible support, to form a latent image of said subjectmatter therein, developing the said latent image in a non-tanningdeveloper to yield an unhardened negative image, exposing the emulsionto light and developing a complementary latent image on the same supportin a tanning developer, transferring the said negative image to a secondflexible support by pressing the said image into intimate contacttherewith at a temperature at which the unhardened emulsion softens andseparating the two supports and thereafter hardening the gelatine of theimage so transferred, the said second flexible support carrying theimage so i transferred constituting a printing plate.

References Cited in the file of this patent UNITED STATES PATENTS1,118,479 Dodge Nov. 24, 1914 1,482,615 John Feb. 5, 1924 2,596,756Yutzy et a1. May 13, 1952 FOREIGN PATENTS 172,342 Great Britain Dec. 5,1921

1. A PHOTOGRAPHIC COPYING PROCESS WHICH COMPRISES EXPOSING TO SUBJECTMATTER TO BE COPIED AN UNHARDENED GELATINO SILVER HALIDE EMULSION ON AFLEXIBLE SUPPORT, TO FORM A LATENT IMAGE OF SAID SUBJECT MATTER THEREIN,DEVELOPING THE SAID LATENT IMAGE IN A NON-TANNING DEVELOPER TO YIELD ANUNHARDENED, NEGATIVE IMAGE, EXPOSING THE EMULSION TO LIGHT ANDDEVELOPING A COMPLEMENTARY LATENT IMAGE ON THE SAME SUPPORT IN A TANNINGDEVELOPER, TRANSFERRING THE SAID NEGATIVE IMAGE TO A SECOND FLEXIBLESUPPORT BY PRESSING THE SAID IMAGE INTO INTIMATE CONTACT THEREWITH AT ATEMPERATURE AT WHICH THE UNHARDENED EMULSION SOFTENS AND SEPARATING THETWO SUPPORTS.